The document discusses the zener diode, emphasizing its design for operation in the reverse-breakdown region and its use as a voltage regulator. It explains two types of breakdown: zener breakdown, which occurs at lower reverse voltages, and avalanche breakdown, which occurs at higher reverse voltages. The zener diode maintains a constant voltage across it in a circuit, making it valuable for providing stable output voltage despite changes in current.

1. Zener Diode
And
As Voltage Regulator

2. BY: Adeel Rasheed

3. Introduction
 The zener diode is a silicon p-n junction devices that
differs from rectifier diodes because it is designed for
operation in the reverse-breakdown region.

4. Circuit of Zener
 One Zener Diode connected with one resistence and
battery.

5. Characteristics
 A Zener diode is always reverse connected
 When forward biased, its characteristics are just like of
ordinary diode
 It has sharp breakdown voltage, called Zener voltage

6. Graph

7. Principle of Zener Diode
 The Working Principle of zener diode lies in the cause of
breakdown for a diode in reverse biased condition. Normally
there are two types of breakdown.
 1) Zener Breakdown
 2) Avalanche Breakdown.

8. Zener Breakdown
 This type of breakdown occurs for a reverse bias voltage between 2 to
8V.
 Even at low voltage, the electric field intensity is strong enough to exert
a force.
 The valence electrons of the atom such that they are separated from the
nuclei.
 This type of break down occurs normally for highly doped diode with
low breakdown voltage and larger electric field.
 As temperature increases, the valence electrons gain more energy to
disrupt from the covalent bond and the less amount of external voltage
is required.
 Thus zener breakdown voltage decreases with temperature.

9. Avalanche Breakdown
 This type of breakdown occurs at the reverse bias voltage
above 8V and higher.
 It occurs for lightly doped diode with large breakdown voltage.
 As minority charge carriers (electrons) flow across the device.
 They tend to collide with the electrons in the covalent bond and
cause the covalent bond to disrupt.

10. Avalanche Breakdown
 As voltage increases, the kinetic energy (velocity) of the
electrons also increases.
 The covalent bonds are more easily disrupted, causing an
increase in electron hole pairs.
 The avalanche breakdown voltage increases with temperature.

11. As Voltage Regulator

12. As Voltage Regulator
 In a DC circuit, Zener diode can be used as a voltage regulator
or to provide voltage reference.
 The main use of zener diode lies in the fact that the voltage
across a Zener diode remains constant for a larger change in
current.
 This makes it possible to use a Zener diode as a constant
voltage device or a voltage regulator.
 In any power supply circuit, a regulator is used to provide a
constant output (load) voltage.

13.  While designing a voltage regulator using zener diode
 The latter is chosen with respect to its maximum power rating.
 The maximum current through the device should be:-
 Imax = Power/Zener Voltage
 Since the input voltage and the required output voltage is
known.
 It is easier to choose a zener diode with a voltage
approximately equal to the load voltage, i.e. Vz ~=Vo.

14.  The value of the series resistor is chosen to be
R =(Vin – Vz)/(Izmin + IL), where IL = Load Voltage/Load
resistance.
 It is advisable to use a forward biased diode in series with the
Zener diode.
 This is because the Zener diode at higher voltage follows the
avalanche breakdown principle, having a positive temperature
of coefficient.
 Hence a negative temperature coefficient diode is used for
compensation.